Today's unprecedented levels of human migration present urgent challenges to traditional conceptualizations of national identity, nation-state sovereignty, and democratic citizenship. Foreigners are commonly viewed as outsiders whose inclusion within or exclusion from "the people" of the democratic state rests upon whether they benefit or threaten the unity of the nation. Against this instrumentalization of the foreigner, this book traces the historical development of the concepts of sovereignty and foreignness through the thought of philosophers such as Plato, Locke, Hobbes, Rousseau, Derrida, and Benhabib in order to show that foreignness is a structural feature of sovereignty that cannot be purged or assimilated.